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Statistical Atlas

Historical Weather For 2012 in Carlsbad, California, USA

Location

This report describes the historical weather record at the McClellan-Palomar Airport (Carlsbad, California, United States) during 2012. This station has records back to December 1972.

Carlsbad, California has a cold semi-arid steppe climate. The area within 25 mi of this station is covered by shrublands (49%), oceans and seas (37%), forests (10%), and built-up areas (5%)

Calendar

Daylight saving time (DST) was observed at Carlsbad, California during 2012. There were two time changes during 2012:

DST started on Sunday March 11, 2012 at 3:00 am, from PST (GMT-8) to PDT (GMT-7).

DST ended on Sunday November 4, 2012 at 1:00 am, from PDT (GMT-7) to PST (GMT-8).

2012 was a leap year and thus has 366 days rather than the normal 365. Leap years occur every fourth year and the extra day is always February 29th. In 2012February 29th falls on a Wednesday.

The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2012 they occurred on:

Spring Equinox

Tuesday, 20 March 2012.

Summer Solstice

Wednesday, 20 June 2012.

Fall Equinox

Saturday, 22 September 2012.

Winter Solstice

Friday, 21 December 2012.

Temperature

The hottest day of 2012 was September 15, with a high temperature of 100°F. For reference, on that day the average high temperature is 73°F and the high temperature exceeds 78°F only one day in ten. The hottest month of 2012 was September with an average daily high temperature of 79°F.

Relative to the average, the hottest day was September 15. The high temperature that day was 100°F, compared to the average of 73°F, a difference of 27°F. In relative terms the warmest month was September, with an average high temperature of 79°F, compared to an typical value of 74°F.

The longest warm spell was from August 6 to August 23, constituting 18 consecutive days with warmer than average high temperatures. The month of September had the largest fraction of warmer than average days with 93% days with higher than average high temperatures.

Temperature

The daily low (blue) and high (red) temperature during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is red where both the daily high and low are above average, blue where they are both below average, and white otherwise.

The coldest day of 2012 was December 19, with a low temperature of 39°F. For reference, on that day the average low temperature is 48°F and the low temperature drops below 43°F only one day in ten. The coldest month of 2012 was January with an average daily low temperature of 48°F.

Relative to the average, the coldest day was December 19. The low temperature that day was 39°F, compared to the average of 48°F, a difference of 9°F. In relative terms the coldest month was July, with an average low temperature of 64°F, compared to an typical value of 64°F.

The longest cold spell was from July 23 to July 31, constituting 9 consecutive days with cooler than average low temperatures. The month of July had the largest fraction of cooler than average days with 58% days with lower than average low temperatures.

Hourly Temperature Bands

The full year of hourly temperature reports with the days of the year on the horizontal and the hours of the day on the vertical. The hourly temperature measurement is color coded into meaningful temperature bands: frigid is purple (below 15°F), freezing is blue (15°F to 32°F), cold is dark green (32°F to 50°F), cool is light green (50°F to 65°F), comfortable is yellow (65°F to 75°F), warm is light red (75°F to 85°F), hot is medium red (85°F to 100°F), sweltering is dark red (above 100°F), and missing data is pink.

Clouds

The clearest month of 2012 was January, with 81% of days being more clear than cloudy. The longest spell of clear weather was from August 6 to August 21, constituting 16 consecutive days that were clearer than they were cloudy.

Cloud Coverage

The fraction of time spent in each of the five sky cover categories over the course of 2012 on a daily basis. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data. The bar at the top of the graph is gray if the sky was cloudy or mostly cloudy for more than half the day, blue if it is clear or mostly clear for more than half the day, and blue-gray otherwise.

The cloudiest month of 2012 was May, with 68% of days being more cloudy than clear. The longest spell of cloudy weather was from November 27 to December 9, constituting 13 consecutive days that were cloudier than they were clear.

Hourly Cloud Coverage

The full year of hourly cloud coverage reports with the days of the year on the horizontal and the hours of the day on the vertical. The sky cover is color coded: from most blue to most gray, the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

Precipitation

This station reports both the quantity of liquid precipitation and categorical observations of precipitation (e.g., moderate rain, or heavy snow). Both are subject to erroneous reports, but the former is particularly prone to false reports, especially ones indicating an excessive quantity of precipitation. Please bear this in mind when reading the extrema reported in this section.

Liquid Equivalent Quantity

The day with the largest quantity of precipitation was December 13. That day saw 0.972" of liquid (or liquid equivalent) precipitation, compared to a median value of 0.031". The month with the most precipitation was December, with 1.945", compared to a median value of 1.396".

As determined by quantitative measurements, the longest dry spell was from May 26 to September 3, constituting 101 consecutive days with no measured precipitation. The months June, July, and August were completely without measured precipitation.

The month with the largest fraction of days with at least some measured precipitation was December, with 52% of days reporting some measured precipitation.

Precipitation Quantity

The daily measured quantity of liquid (or liquid equivalent in the case of solid precipitation) precipitation over the course of 2012, with the median non-zero quantity (thick gray line) and 10th, 25th, 75th, and 90th non-zero percentiles (shaded areas). The bar at the top of the graph is green if any precipitation was measured that day and white otherwise.

Present Weather Reports

This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.

The day in 2012 with the most precipitation observations was December 13. There were 12 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was December, with 34 hourly present weather reports involving some form of precipitation.

Precipitation Reports

The daily number of hourly observed precipitation reports during 2012, color coded according to precipitation type, and stacked in order of severity. From the bottom up, the categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); and drizzle (lightest green). Not all categories are necessarily present in this particular graph. The faint shaded areas indicate climate normals. The bar at the top of the graph is green if any precipitation was observed that day and white otherwise.

As determined by the present weather reports, the longest dry spell was from April 27 to July 13, constituting 78 consecutive days with no observed precipitation. The months May, June, and August were completely without observed precipitation.

The month with the largest fraction of days with at least some observed precipitation was December, with 29% of days reporting some observed precipitation.

Hourly Weather Reports

The full year of hourly present weather reports with the days of the year on the horizontal and the hours of the day on the vertical. The color-coded categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); drizzle (lightest green); freezing rain and sleet (light and dark cyan); snow grains (lightest blue); hail (red); fog (gray); and haze (brownish gray).

Snow

Either snow is exceptionally rare at this location or this station did not reliably report it during 2012.

Humidity

Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.

When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of 2012 was January with an average daily low humidity of 36%, and the most humid month was July with an average daily low humidity of 66%.

But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.

Humidity

The daily low (brown) and high (blue) relative humidity during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Dew Point

Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.

Generally speaking, dew points below 50°F will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 50°F to 68°F are fairly comfortable to most people, and dew points above 68°F are increasingly uncomfortable, becoming oppressive around 77°F.

To take some examples, and basing our categorization on the daily high dew point in 2012, January had 15 dry days, 16 comfortable days, and no humid days; April had 6 dry days, 24 comfortable days, and no humid days; July had no dry days, 31 comfortable days, and no humid days; and October had 2 dry days, 28 comfortable days, and 1 humid day.

Dew Point

The daily low (blue) and high (red) dew point during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind Speed

Visibility

Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.

The day of 2012 with the lowest average visibility was December 8, with an average visibility of 2.5 mi. The month with the lowest average visibility was November, with an average visibility of 8.1 mi. With an average visibility of 9.5 mi, the month of March had the highest average visibility.

Visibility

The daily average visibility, depicted as gray bars encroaching down from the top of the graph.

Cloud Ceiling

The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.

The day of 2012 with the lowest average cloud ceiling was January 2, with an average cloud ceiling of 98'. The month with the lowest average cloud ceiling was June, with an average cloud ceiling of 1129'. The month of February has the highest average cloud ceiling, with an average cloud ceiling of 3000'.

Cloud Ceiling

The daily average cloud ceiling, depicted as gray bars encroaching down from the top of the graph. Missing data or days with insufficient clouds to define a cloud ceiling are shown as white columns.